Historically, .22 has always been the best selling calibre. Consequently .177's are that bit rarer, so command a better price once the gun becomes "collectable". Look at any two comparable Webley pistols and you'll notice the one in .177 calibre is always priced a little higher.
Whether or not this will be true of the "Centenial" Tempest by the time it becomes collectible; who knows? I'd have liked to have seen this pistol have special commemorative stamps on the actual pistol seeing as it's meant to be a limited edition. As it stands, if what now calls itself Webley decide to do this pistol as an ordinary production gun at some point in the future there'll be no visible difference between the commemorative and the standard. So apart from having a nice looking case, why would I want to pay £200 for one?
The South of England has 2 good things, the M1 and the A1. Both will take you to Yorkshire.